Fabrics with functional properties have been disclosed for use in textile yarns. Examples include metallic yarns that can be used for carrying electrical current, performing an anti-static electricity function, or providing shielding from electric fields. Such yarns or fibers can, for example, include: multifilament stainless steel yarns; metallized aramid fibers; optical fibers for transmitting electrical data by acting as light waveguides; and glass or silica fibers for dielectric high frequency applications, Such highly functional yarns have been fabricated into fabrics, garments and apparel articles.
It is generally considered to be impractical to base a textile yarn solely on such high modulus filaments or on a combination yarn where the high modulus filaments are required to be a flex member of the yarn. Such high modulus filaments can typically be expected to exhibit low bending capability and poor flexibility.
Sources of stainless steel continuous multifilament fibers typically used in textiles include, but are not limited to: NV Bekaert SA, Kortrijk, Belgium; and Sprint Metal Groupe Arcelor, France. Depending on the number of filaments and the number of twisted yarns involved, these yarns usually have a filament diameter from about 6 μm to about 12 μm, and an electrical resistivity in the range of about 2 Ohm/m to about 70 Ohm/m. In general, these metal fibers exhibit a high force to break, typically in the range of about 20 N to about 500 N and relativity little elongation, typically less than about 5%. However, these fibers exhibit substantially no elasticity. In contrast, many elastic synthetic polymer based textile yarns stretch to at least about 125% of their unstressed specimen length and recover more than about 50% of this elongation upon relaxation of the stress.
Sources of plastic optical fibers for use in textiles include, but are not limited to: Toray Industries, Inc.; Mitsubishi Corporation; and Asahi Chemical. Typically, these fibers have diameters of about 0.5 to about 2 mm. Due to their construction, such fibers have the ability to transmit light along their length via total internal reflection, which light can then be converted into electrical energy or signals. This property of optical fibers tends to make them advantageous as compared to metal wires or coaxial transmission for data signal transmission, especially due to their relatively higher bandwidth, lower attenuation, lower noise, and lower cost.
Sources of metallized fibers include metallic coatings added on the surface of aramid fibers, such as Aracon® manufactured and sold by E.I. DuPont de Nemours. These yarns are based on stranded Kevlar® fibers, having an equivalent diameter to metal wire of about 54 AWG and electrical resistivity in the range of about 2 Ohms/m to about 9 Ohms/m. In general, these metallic fibers have a load to break of about 27 N to about 70 N and an elongation to break of less than about 5%.
Sources of inorganic quartz or silica fibers for use in textiles include, but are not limited to those made by Saint-Gobain (France). These fibers generally have filament diameters of about 1 μm to about 25 μm, a dielectric constant in the range of about 3 to about 7 in the frequency range up to about 10 GHz, and a loss tangent of about 0.0001 to about 0.0068 in the frequency range up to about 10 GHz. In general, these fibers exhibit a high tensile strength in the range of about 2000 N/mm2 to about 6000 N/mm2, high tensile modulus of about 50,000 N/mm2 to about 90,000 N/mm2, and relativity little elongation of about 2 to about 8%.
State of the Art: Plastic Optical Fibers in Textiles
Woven fabrics made by incorporation of optical fibers are known in the art. Typically, such optical fibers have an internal core and an external sheath. The external sheath has a lower refractive index compared to the internal core, which causes total internal reflection of light so that light travels solely through the internal core of the fiber. Light may be caused to escape from the surface of the fiber, thus creating an illuminating effect. There are two major directions disclosed for such effect: (1) attack of the fiber surface (mechanical or chemical), (2) deformation or bending of the fiber, at discrete locations along the fiber length.
(1) State-of-the-art Illumination by Optical Fibers Via Mechanical Attack
U.S. Pat. No. 4,234,907 to Maurice, discloses a light-emitting fabric woven with optical fibers for use in clothing, interior, or technical textiles. Optical fibers are woven in the warp direction crossed with normal textile fibers as weft threads. The optical fibers are illuminated at one end by a light source. Illumination from the surface of the fiber is achieved by making notches at the cladding till the inner core, the spacing of which becomes narrower as the distance from the light source increases so that there is a uniform distribution of light across the fabric. Analysis or such fabric makes it unsuitable for industrial manufacturing, as the notches weaken the fiber, making textile processing impossible, while the bundling of all fiber ends into a light source would require extreme fiber length extending out of the fabric.
WO 02/12785 A1 to Givoletti, discloses a textile incorporating illuminated fibers. The fibers consist of a central core capable of transmitting light and of an external sheath that presents a refractive index, which in respect to the internal core, allows the transmitted light to escape partially from the fiber. Illumination is achieved by texturing the fibers (via e.g. abrasions, scratching), adding doping elements inside the fiber that modify the diffusion angle of light, modifying the refractive index of the cladding so as to disperse the light along the fiber, and modifying the reflective index of the optical fibers by fabric treatment through mechanical or chemical means. Further the reference discloses a special woven construction that illuminates light uniformly.
WO 02/068862A1 to Deflin et al., discloses a lighting device based on optical fibers with light-emitting segments, a possible structure of such a device including optical fibers that are woven into a textile together with other textile fibers. In 2002, France Telecom won the Avantex Innovation Prize for the presentation of a first flexible display based on an optical fiber fabric (E. Deflin, et. al., “Communicating Clothes: Optical Fiber Fabric for a New Flexible Display”, 2nd International Avantex Symposium, Frankfurt, Germany). Optical fibers were processed via a special process of fiber surface mechanical attack, disclosed in PCT/FR94/01475, to A. Bernasson, et al., allowing for light to be scattered throughout the outer surface of the fibers at controlled locations on the length of the fiber. The fibers were then woven into a fabric. They were lighted through LEDs that could be used to light groups of fibers, each group representing one pixel of the matrix. By controlling the matrix through wireless telecommunication services, various patterns can be generated in the cloth, hence providing for an intelligent display. Although fine fiber diameters were used (about 0.5 mm), it was not optimal to create an X-Y network by introducing the fibers both in the weft and warp directions, as the fabric would be very rigid and the grid not very dense. Therefore, such fabrics would not be appropriate for typical clothing applications, where flexibility and freedom of movement of the fabric are of paramount importance. Further, special processing of the fibers is needed to transmit light from the surface of the optical fiber.
WO 2004/057079A1 to Laustsen, discloses a woven fabric with optical fibers that goes beyond the disclosure of U.S. Pat. No. 4,234,907 by allowing optical fibers to extend in mutually crossing directions in the fabric. According to the Laustsen reference, the fabric is hot rolled to compress and flatten the light guides, and further is laser treated to create partial ruptures at the surface of the optical fibers.
(2) State-of-the-art Illumination by Optical Fibers Via Bending
U.S. Pat. Nos. 4,885,663, 4,907,132, 5,042,900, and 5,568,964 to Parker et al., disclose fiber optic light emitting panel assemblies made of woven optical fibers. Light is caused to be transmitted from the optical fiber surfaces by deforming or bending the optical fibers at discrete locations along their length such that the angle of bend exceeds the angle of internal reflection. The optical fibers are typically woven in the warp direction, while till threads are woven in the weft direction, although the fill threads are also allowed to be optical fibers. The output pattern of light is achieved by controlling the weave spacing and pattern of the optical fibers and fill threads. A portion of the light emitting area is sealed by adhering the optical fibers and fill threads together to hold the fill threads in position and keep the optical fibers from separating from the light emitting portion.
UK 2,361,431A to Whitehurst, discloses a fiber optic fabric for phototherapy, wherein light emitted from the surface of the optical fibers (including plastic and glass optical fibers) is directed towards a patient for the treatment of large area skin conditions for therapy, or cosmetic treatment. The inventor found that by weaving the optical fiber together with other fill yarns, the optical fiber bending around the fill fibers causes light to be refracted out of the optical fiber and hence out of the fabric. It is disclosed that when a large number of optical fibers is woven in this way, the fabric will emit light in a generally uniform distribution across the fabric. For the use of the fabric for phototherapy, it is very important that the fabric has flexibility to provide the necessary movement and comfort for the user, and that it follows the skin area that needs to be protected. However, it is known that fabrics based on optical fibers are rigid and tough for wearable clothing and wilt generally not allow movement of the fabric in the direction of optical fibers. Therefore, such a fabric may not provide for the desired flexibility or be optimum for the intended application.
(3) State-of-the-art Optical Fibers for Signal Transmission
U.S. Pat. No. 6,381,482B1 to Jayaraman et al., discloses a tubular knitted or woven fabric, or a woven or knitted 2-dimensional fabric, including integrated flexible information infrastructure for collecting, processing, transmitting, and receiving information concerning a wearer of the fabric. The fabric consists of a base fabric providing for wear comfort and an information component, which includes sheathed plastic optical fiber to provide a penetration detection means as well as data transferring information. The fabric, consisting of the optical fibers, is then integrated into a garment structure by joining techniques such as sewing, gluing or attachment.
Optical fibers as sensors have also been used in textile composites to distribute sensing locally (point) or multiplexed (multi-point) exploiting intensiometric, interferometric, or Bragg grating principles. See X. M. Tao, J. Text. Inst. 2000, Vol 91 Part 1, No. 3, pp 448-459; and W. C. Du et al., J. Compos. Struct. Vol 42, pp. 217-230, (1998). Optical fibers can provide an effective means to determine quantitatively the distribution of physical parameters (e.g., temperature, stress-strain, pressure), and therefore may find uses in smart structures applications, such as monitors of manufacturing processes and internal-health conditions. In these developments, the embedded optical fibers also act as signal-transmission elements.
Stretch and recovery is considered to be an especially desirable property of a yarn, fabric or garment, which is also able to conduct electrical current, transmit data processing information, illuminate, sense, and/or provide electric field shielding. The stretch and recovery property, or “elasticity”, is the ability of a yarn or fabric to elongate in the direction of a biasing force (in the direction of an applied elongating stress) and return substantially to its original length and shape, substantially without permanent deformation when the applied elongating stress is relaxed. In the textile arts, it is common to express the applied stress on a textile specimen (e.g., a yarn or filament) in terms of a force per unit of cross section area of the specimen or force per unit linear density of the unstretched specimen. The resulting strain (elongation) of the specimen is expressed in terms of a fraction or percentage of the original specimen length. A graphical representation of stress versus strain is the stress-strain curve, which is well-known in the textile arts.
The degree to which a fiber, yarn, or fabric returns to the original specimen length prior to being deformed by an applied stress is called “elastic recovery”. In stretch and recovery testing of textile materials, it is also important to note the elastic limit of the test specimen. The elastic limit is the stress load above which the specimen shows permanent deformation. The available elongation range of an elastic filament is that range of extension throughout which there is no permanent deformation. The elastic limit of a yarn is reached when the original test specimen length is exceeded after the deformation inducing stress is removed. Typically, individual filaments and multifilament yarns elongate (strain) in the direction of the applied stress. This elongation is measured at a specified load or stress. In addition, it is useful to note the elongation at break of the filament or yarn specimen. This breaking elongation is that fraction of the original specimen length to which the specimen is strained by an applied stress which ruptures the last component of the specimen filament or multifilament yarn. Generally, the drafted length is given in terms of a draft ratio equal to the number of times a yarn is stretched from its relaxed unit length.
Elastic fabrics having conductive wiring affixed to the fabric for use in garments intended for monitoring of physiological functions in the body are disclosed in U.S. Pat. No. 6,341,504 to Istook. This patent discloses an elongated band of elastic material stretchable in the longitudinal direction and having at least one conductive wire incorporated into or onto the elastic fabric band. The conductive wiring in the elastic fabric band is formed in a prescribed curved configuration, e.g., a sinusoidal configuration. This elastic conductive band is able to stretch and alter the curvature of the conduction wire. As a result, the electrical inductance of the wire is changed. This property change is used to determine changes in physiological functions of the wearer of a garment including such a conductive elastic band. The elastic band is formed in part using an elastic material, preferably spandex. Filaments of the spandex material, sold by INVISTA® North America Sà r. I., Wilmington, Del., under the trademark LYCRA®, are disclosed as being a desirable elastic material. Conventional textile means to form the conductive elastic band are disclosed, including: warp knitting, weft knitting, weaving, braiding, and non-woven construction. Other textile filaments, in addition to metallic filaments and spandex filaments, are included in the conductive elastic band. These other filaments include nylon and polyester.
While elastic conductive fabrics with stretch and recovery properties dominated by a spandex component of the composite fabric band have been disclosed, these conductive fabric bands are intended to be discrete elements of a fabric construction or garment used for prescribed physiological function monitoring. Although such elastic conductive bands may have advanced the art in physiological function monitoring, they have not been shown to be satisfactory for use in a way other than as discrete elements of a garment or fabric construction.
In view of the foregoing, it is believed desirable to provide high modulus functional textile yarns, including but not limited to conductive, fiber optic, and glass fibers, wherein such textile yarns have elastic recovery properties that can be processed using traditional textile means to produce knitted, woven, or nonwoven fabrics (“elastic functional yarns”). Further, it is believed that there is yet a need for fabrics and garments that are substantially constructed from such elastic functional yarns. Fabrics and garments substantially constructed from elastic functional yarns can provide stretch and recovery characteristics to the entire construction, conforming to any shape, any shaped body, or requirement for elasticity. It is further believed desirable to provide controlled loops (bends) of such high modulus functional fibers, either individually or within the fabric construction, so as to provide for special illumination effects, as in the case of optical fibers, or special electrical signals, as in the case of conductive fiber loops for inductive signal generation and transmission.